How to Install macOS 10.12 Sierra on a Separate Partition & Dual-Boot

WWDC 2016 has come to a close, and with it came a new version of macOS. The beta version of macOS 10.12 Sierra has been released to developers. However as this is only a beta version it is bound to have a lot of bugs. For this reason it possibly isn’t the best idea to install it over your current macOS version. If you want to be able to use and test macOS 10.12 without updating your current OS to it, you can install it on a separate drive partition or external drive.

Select the drive you want to install macOS on. At the top you should see a ‘Partition’ button. Click it, click the + sign and make set the new partition to be at least 20GB in size. Make sure the format is set to Mac OS Extended (Journaled) volume with a GUID Partition Table. Give it a name and click ‘Apply’. Once this is done you will have a extra partition on your drive.

Open the macOS 10.12 file you downloaded. If it is a .dmg the installer will be inside it. Open the installer.

Run through the installer until you are asked where you want to install macOS. Make sure you select the partition you created in disk utility. Then click next. macOS 10.12 will now begin to install on that partition.

Once the install is complete you Mac will boot into the newly install OS. To boot from the partition in future, hold down the Alt/Option key while booting. You will then be asked which drive to boot from. Select the partition with macOS 10.12 installed.